pi package:dimensional

pi :: Floating a => Dimensionless a
dimensional Numeric.Units.Dimensional Numeric.Units.Dimensional.Prelude
pi :: (Integral a, KnownExactPi s) => SQuantity s DOne a
dimensional Numeric.Units.Dimensional.FixedPoint
pico :: Fractional a => Unit 'Metric d a -> Unit 'NonMetric d a
dimensional Numeric.Units.Dimensional.SIUnits
The "pico" prefix, denoting a factor of 10^-12.
imperialPint :: Fractional a => Unit 'NonMetric DVolume a
dimensional Numeric.Units.Dimensional.NonSI
One imperial pint is one half of an imperialQuart. See here for further information. 
>>> 1 *~ imperialPint
5.6826125e-4 m^3

>>> 1 *~ imperialPint :: Volume Rational
454609 % 800000000 m^3
usPint :: Fractional a => Unit 'NonMetric DVolume a
dimensional Numeric.Units.Dimensional.NonSI
One US liquid pint is one half of a usQuart. See here for further information. 
>>> 1 *~ usPint
4.73176473e-4 m^3

>>> 1 *~ usPint :: Volume Rational
473176473 % 1000000000000 m^3